Two people briefed on the probe say the FDA is focusing its investigation on lettuce grown in Arizona as a possible source for an E. coli outbreak.
At least 19 people in Ohio, New York and Michigan have been sickened, including students on three college campuses, prompting a recall throughout much of the country.
Freshway Foods of Sidney, Ohio, said it was recalling romaine lettuce sold under the Freshway and Imperial Sysco brands in 23 states and the District of Columbia.
The FDA says three of those sickened were hospitalized with life-threatening symptoms. The federal Centers for Disease Control and Prevention says it's looking at 10 other cases probably linked to the outbreak.
The New York state Public Health Laboratory in Albany discovered the contamination in a bag of Freshway Foods shredded romaine lettuce on Wednesday.
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